The invention relates to routing in ad hoc telecommunications networks.
An ad hoc telecommunications network is a network in which mobile units called nodes are free to move and to communicate wirelessly with one another.
These networks have the advantage of being very flexible, each mobile unit being adapted to route traffic in order to create paths between the nodes.
However, it is very difficult to achieve efficient routing in an ad hoc network that includes a large number of nodes.
One known approach to solving this scalability problem integrates ad hoc networks and fixed networks, for example IP networks.
The result is called a hybrid network.
Thus, as known in the art, a hybrid network is primarily composed of ad hoc networks interconnected by a fixed infrastructure network, the interface between an ad hoc network and the fixed infrastructure network being provided by units known interchangeably as gateways or access points.
When a message is to be routed between two nodes of an ad hoc network, the best path between those nodes is determined, and may optionally pass through the gateway.
A gateway discovery problem arises in a hybrid telecommunications network at the nodes of the ad hoc network requiring access to the fixed infrastructure network.
In a so-called proactive scheme, the gateway periodically broadcasts advertisement messages over the ad hoc network to provide the nodes of that network with information for identifying a path to the gateway. These proactive schemes offer good connectivity but have often been criticized because they occupy bandwidth in the ad hoc network unnecessarily, especially when some nodes do not need connectivity with the fixed network.
In a so-called reactive scheme, only nodes that need to access the fixed infrastructure network seek to identify a gateway by broadcasting a solicitation message in the network. In that scheme, bandwidth is used inefficiently if a large number of nodes require connectivity with the fixed network.
Also known in the art are hybrid schemes that exploit the advantages of proactive and reactive schemes. In those hybrid schemes, the gateway broadcasts the advertisement messages periodically but, in contrast to proactive schemes, the messages are not broadcast throughout the network, but only to a particular depth expressed as a plurality of hops from the gateway.
A first problem is to determine the depth and the period between two successive broadcasts of the advertisement message.
Moreover, it is clear that the mobile nodes situated nearby, and especially those located one hop from the gateway, are heavily loaded by traffic between the other nodes of the network and the fixed infrastructure.
That represents a major drawback if those nodes do not have sufficient capacity to support the traffic.